Auto-Injector

ABSTRACT

Auto-injector for administering a dose of a liquid medicament includes a housing to contain a syringe with a hollow needle and a stopper for sealing the syringe and displacing the medicament (M), the housing having a distal end (D) and a proximal end (P) with an orifice to apply against an injection site. A spring means, upon activation, can push the needle from inside the housing through the orifice and past the proximal end (P), operate the syringe to supply the dose of medicament (M), and retract the syringe with the needle after delivering the medicament (M). An activating means can lock the spring means in a pressurized state prior to manual operation and capable of, upon manual operation, releasing the spring means for injection.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/165,720, filed May 26, 2016, which is a continuation of U.S.patent application Ser. No. 13/806,324 filed Dec. 21, 2012, which is aU.S. National Phase Application pursuant to 35 U.S.C. § 371 ofInternational Application No. PCT/EP2011/060726 filed Jun. 27, 2011,which claims priority to European Patent Application No. 10167506.4filed Jun. 28, 2010. The entire disclosure contents of theseapplications are herewith incorporated by reference into the presentapplication.

TECHNICAL FIELD

The invention relates to an auto-injector for administering a dose of aliquid medicament according to the preamble of claim 1.

BACKGROUND

Administering an injection is a process which presents a number of risksand challenges for users and healthcare professionals, both mental andphysical.

Injection devices (i.e. devices capable of delivering medicaments from amedication container) typically fall into two categories—manual devicesand auto-injectors.

In a manual device—the user must provide the mechanical energy to drivethe fluid through the needle. This is typically done by some form ofbutton/plunger that has to be continuously pressed by the user duringthe injection. There are numerous disadvantages to the user from thisapproach. If the user stops pressing the button/plunger then theinjection will also stop. This means that the user can deliver anunderdose if the device is not used properly (i.e. the plunger is notfully pressed to its end position). Injection forces may be too high forthe user, in particular if the patient is elderly or has dexterityproblems.

The extension of the button/plunger may be too great. Thus it can beinconvenient for the user to reach a fully extended button. Thecombination of injection force and button extension can causetrembling/shaking of the hand which in turn increases discomfort as theinserted needle moves.

Auto-injector devices aim to make self-administration of injectedtherapies easier for patients. Current therapies delivered by means ofself-administered injections include drugs for diabetes (both insulinand newer GLP-1 class drugs), migraine, hormone therapies,anticoagulants etc.

Auto-injectors are devices which completely or partially replaceactivities involved in parenteral drug delivery from standard syringes.These activities may include removal of a protective syringe cap,insertion of a needle into a patient's skin, injection of themedicament, removal of the needle, shielding of the needle andpreventing reuse of the device. This overcomes many of the disadvantagesof manual devices. Injection forces/button extension, hand-shaking andthe likelihood of delivering an incomplete dose are reduced. Triggeringmay be performed by numerous means, for example a trigger button or theaction of the needle reaching its injection depth. In some devices theenergy to deliver the fluid is provided by a spring.

US 2002/0095120 A1 discloses an automatic injection device whichautomatically injects a pre-measured quantity of fluid medicine when atension spring is released. The tension spring moves an ampoule and theinjection needle from a storage position to a deployed position when itis released. The content of the ampoule is thereafter expelled by thetension spring forcing a piston forward inside the ampoule. After thefluid medicine has been injected, torsion stored in the tension springis released and the injection needle is automatically retracted back toits original storage position.

The spring means is a single compression spring arranged to be groundedat a distal end in the housing for advancing the needle and forinjecting the dose of medicament via a plunger and wherein thecompression spring is arranged to have its ground in the housingswitched to its proximal end for retracting the syringe.

SUMMARY

It is an object of the present invention to provide an improvedauto-injector.

The object is achieved by an auto-injector according to claim 1.

Preferred embodiments of the invention are given in the dependentclaims.

In the context of this specification the term proximal refers to thedirection pointing towards the patient during an injection while theterm distal refers to the opposite direction pointing away from thepatient.

According to the invention, an auto-injector for administering a dose ofa liquid medicament comprises:

-   -   an elongate housing arranged to contain a syringe with a hollow        needle and a stopper for sealing the syringe and displacing the        medicament, the housing having a distal end and a proximal end        with an orifice intended to be applied against an injection        site, wherein the syringe is slidably arranged with respect to        the housing,    -   spring means capable of, upon activation:    -   pushing the needle from a covered position inside the housing        into an advanced position through the orifice and past the        proximal end,    -   operating the syringe to supply the dose of medicament, and    -   retracting the syringe with the needle into the covered position        after delivering the medicament,    -   activating means arranged to lock the spring means in a        pressurized state prior to manual operation and capable of, upon        manual operation, releasing the spring means for injection.

According to the invention the spring means is a single drive spring inthe shape of a compression spring arranged to be grounded at a distalend in the housing for advancing the needle and for injecting the doseof medicament. The force of the drive spring is forwarded to the needleand/or the syringe via a plunger. The drive spring is arranged to haveits ground in the housing switched to its proximal end for retractingthe syringe when the injection of the medicament is at least nearlyfinished.

The single drive spring is used for inserting the needle, fully emptyingthe syringe and retracting the syringe and needle to a safe positionafter injection. Thus a second spring for withdrawing the syringe andneedle, which is a motion with an opposite sense compared to advancingthe syringe and injecting the dose, is not required. While the distalend of the drive spring is grounded the proximal end moves the syringeforward for inserting the needle and carries on to the injection bypushing on the stopper. When the injection is at least nearly finishedthe drive spring bottoms out at its proximal end, resulting in theproximal end being grounded in the housing. At the same time the distalend of the drive spring is released from its ground in the housing. Thedrive spring is now pulling the syringe in the opposite direction.

According to the invention the activating means is arranged as a triggerbutton laterally arranged on the housing. A lateral trigger button canbe easier to operate for people with dexterity problems.

The auto-injector according to the invention has a particularly low partcount compared to most conventional auto-injectors. The use of just onedrive spring reduces the amount of metal needed and thus consequentlyreduces weight and manufacturing costs.

The trigger button is preferably pivoted in the housing and arranged tobe rotated when operated.

An interlock sleeve may be telescoped in the proximal end of thehousing, the interlock sleeve translatable in longitudinal directionbetween a proximal position and a distal position and biased in proximaldirection in a manner to protrude from the housing in the proximalposition. The interlock sleeve is arranged to be translated from itsproximal position into an intermediate position when pressed against theinjection site. The trigger button is arranged to push the interlocksleeve from the intermediate position into the distal position thusreleasing the drive spring. Before the syringe and needle translate inproximal direction the activating means, i.e. the lateral trigger buttonhas to be operated so as to release the drive spring. The probabilityfor inadvertent operation of the auto-injector thus decreases due to therequirement of two user actions, pressing the auto-injector against theinjection site and operating the trigger button.

In its proximal position the interlock sleeve may be arranged to holdthe trigger button in a depressed position, e.g. flush with the housing.Translation of the interlock sleeve into the intermediate positioncauses the trigger button to emerge from the housing into a readyposition. This provides a sequenced operation in a manner that thetrigger button cannot be operated before the interlock sleeve is pressedagainst the injection site.

It is desirable to trigger the retraction of the needle when thecontents of the syringe have been entirely delivered to the patient,i.e. when the stopper has bottomed out in the syringe. Automaticallytriggering the retraction when the stopper exactly reaches the end ofits travel is a problem due to tolerances when manufacturing the syringeand stopper. Due to these tolerances the position of the stopper at theend of its travel relative to the retracting means is not repeatable.Consequently, in some cases the stopper would prematurely bottom out sothe retraction would not be triggered at all. In other cases theretraction would be triggered before the stopper bottomed so residualmedicament would remain in the syringe.

The retraction could automatically be triggered a certain amount of timeor travel before the stopper bottoms out in the syringe. However thisreliable retraction would be traded off for residual medicament in thesyringe.

Thus, in a preferred embodiment the interlock sleeve is furthermorearranged to prevent release of the distal ground of the drive springwhen in its intermediate and/or distal position. This means, the drivespring remains distally grounded as long as the auto-injector is keptpressed against the injection site so the needle retraction can onlystart when the auto-injector is removed from the injection site and theinterlock sleeve consequently returns into its proximal position andthus releases the distal ground.

A retraction sleeve may be axially movable arranged in the housing,wherein the drive spring is arranged inside the retraction sleeve withits distal end bearing against a distal end face and with its proximalend bearing against a thrust face of a decoupling member. A resilientlug on the interlock sleeve is arranged to be engaged with theretraction sleeve by the trigger button being depressed when theinterlock sleeve is in its intermediate or distal position so as toprevent the retraction sleeve from translating in distal direction.Thus, when the interlock sleeve is pressed against the injection site,the retraction sleeve is kept from retracting. Only after removal of theauto-injector from the injection site and consequent translation of theinterlock sleeve into its proximal position the retraction sleeve maytranslate in distal direction and retract the needle into the housing.

The lug may be engaged between two ramps on the trigger button in such amanner that the trigger button is pulled into the depressed positionupon translation of the interlock sleeve into its proximal position bythe lug sliding along the first ramp. The trigger button is pushed intoits ready position by the lug sliding along the second ramp.

A third ramp may be arranged on the interlock sleeve for being engagedby a pin on the trigger button when the trigger button is being pressedwhen the interlock sleeve is in its intermediate position. When thetrigger button is being pressed the pin slides along the third ramp andtranslates the interlock sleeve into its distal position for triggeringthe injection.

A tubular syringe carrier may be arranged for holding the syringe andsupporting it at its proximal end. Supporting the syringe at theproximal end is preferred over support at the finger flanges since thefinger flanges are more frangible under load while the proximal or frontend of the syringe is more robust. The syringe and the syringe carrierare arranged for joint axial translation. The syringe carrier istelescoped in the interlock sleeve.

In a preferred embodiment at least one latch is provided for axiallyfixing the retraction sleeve in a maximum proximal position. Thedecoupling member is arranged to decouple the latch when being moved inproximal direction nearly into a maximum proximal position. Whendecoupled, the retraction sleeve is allowed to move in distal directionand retract the needle by means of the spring force which is no longergrounded at its distal end. Thus, retraction can only occur if thelatches have been released and if the auto-injector has been removedfrom the injection site.

Preferably the plunger is arranged for pushing the syringe and/or thestopper in proximal direction. At least one but preferably two or moreresilient decoupling arms are arranged at the decoupling member. Thedecoupling arms exhibit inner ramped surfaces bearing against a firstshoulder of the plunger in proximal direction. The resilient decouplingarms are supportable by an inner wall of the retraction sleeve in orderto prevent the decoupling arms from being flexed outward and slip pastthe first shoulder. In this state the plunger may be pushed in proximaldirection by the decoupling member pushing against the first shoulder inorder to insert the needle and inject the dose. At least one aperture isarranged in the retraction sleeve allowing the decoupling arms to beflexed outward by the first shoulder thus allowing the first shoulder toslip through the decoupling arms in proximal direction. This may happenwhen the injection is at least nearly finished. The decoupled plungerallows the syringe and needle to be retracted since it is no longerbearing against the decoupling member.

The syringe may be arranged for joint axial movement with a syringeholder which is slidably arranged in the retraction sleeve. The syringeholder is provided with at least two resilient syringe holder armsarranged distally, the syringe holder arms having a respective inclinedsurface for bearing against a second shoulder, which is arranged at theplunger proximally from the first shoulder. The syringe holder arms aresupportable by an inner surface of the housing in order to prevent themfrom being flexed outward. Thus, when the trigger button is pressed thespring force forwarded by the plunger does not yet press against thestopper but against the syringe for forwarding it. Consequently, a socalled wet injection is avoided, i.e. the liquid medicament is notleaking out of the hollow needle before the needle is inserted. Awidened portion is provided in the housing for allowing the syringeholder arms to flex outwards when the syringe holder has nearly reacheda maximum proximal position thus allowing the second shoulder to slipthrough the syringe holder arms and to switch load of the drive springfrom the syringe to the stopper. This allows for defining the moment tostart injecting the medicament.

The syringe holder may have at least one stop for being engaged by aresilient first clip on the housing in a manner to prevent translationof the syringe holder in proximal direction. The first clip may bearranged to decouple from the stop upon translation of the interlocksleeve into its distal position in order to release the drive spring andstart the injection.

Usually the hollow needle is equipped with a protective needle shieldfor keeping the needle sterile and preventing it from being mechanicallydamaged. The protective needle shield is attached to the needle when theauto-injector or the syringe is assembled.

Preferably a cap is provided at the proximal end of the housing. A sheetmetal clip is attached to the cap for joint axial movement andindependent rotation. The sheet metal clip is arranged to extend throughan orifice into the interlock sleeve when the cap is attached to theinterlock sleeve. The sheet metal clip incorporates at least two barbssnapped into a circumferential notch or behind a shoulder of theprotective needle shield. This allows for automatically engaging thesheet metal clip with the protective needle shield during assembly. Whenthe cap is removed from the interlock sleeve in preparation of aninjection the protective needle shield is reliably removed withoutexposing the user too high a risk to injure themselves.

The cap may be attachable to the housing by a screw connection. Thisallows for a low force removal of the protective needle shield.

The housing may have at least one viewing window for inspecting thesyringe.

The auto-injector may preferably be used for subcutaneous orintra-muscular injection, particularly for delivering one of ananalgetic, an anticoagulant, insulin, an insulin derivate, heparin,Lovenox, a vaccine, a growth hormone, a peptide hormone, a proteine,antibodies and complex carbohydrates.

The cap with the sheet metal spring may also be applied with otherauto-injectors and injection devices.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus, are not limitiveof the present invention, and wherein:

FIGS. 1A-B are two longitudinal sections of an auto-injector with asingle drive spring for advancing a syringe with a needle, injecting adose of medicament and retracting the syringe and needle, theauto-injector as-delivered,

FIG. 2 is a longitudinal section of the auto-injector with a skininterlock sleeve translated in distal direction and a lateral triggerbutton ready to be operated, and

FIG. 3 is a detail of the auto-injector with the trigger buttondepressed.

Corresponding parts are marked with the same reference symbols in allfigures.

DETAILED DESCRIPTION

FIGS. 1A-B show two longitudinal sections in different section planes ofan auto-injector 1, the different section planes approximately 90°rotated to each other. The auto-injector 1 comprises an elongate housing2. A syringe 3, e.g. a Hypak syringe, with a hollow needle 4 is arrangedin a proximal part of the auto-injector 1. When the auto-injector 1 orthe syringe 3 is assembled a protective needle shield may be attached tothe needle (not illustrated). A stopper 6 is arranged for sealing thesyringe 3 distally and for displacing a liquid medicament M through thehollow needle 4. The syringe 3 is held in a tubular syringe carrier 7and supported at its proximal end therein. A single drive spring 8 inthe shape of a compression spring is arranged in a distal part of theauto-injector 1. A plunger 9 is arranged for forwarding the spring forceof the drive spring 8.

Inside the housing 2 a retraction sleeve 10 is slidably arranged. Beforethe injection is triggered the retraction sleeve 10 is in a maximumproximal position and prevented from moving in distal direction D bymeans of stops 11 caught behind latches 12 in the housing 2. A distalend of the drive spring 8 bears against an end face 13 of the retractionsleeve 10. Due to the stops 11 and latches 12 the force of the drivespring 8 is reacted into the housing 2. The proximal end of the drivespring 8 bears against a decoupling member 14 arranged around theplunger 9.

The decoupling member 14 comprises a thrust face 17 for bearing againsta proximal end of the drive spring 8. Proximally from the thrust face 17two or more resilient decoupling arms 18 are provided at the decouplingmember 14, the decoupling arms 18 having inner ramped surfaces bearingagainst a first shoulder 19 in the plunger 9 in proximal direction P.The resilient decoupling arms 18 are supported by an inner wall of theretraction sleeve 10 in this situation so they cannot flex outward andslip past the first shoulder 19.

The syringe carrier 7 is engaged for joint axial movement with a syringeholder 22 which is slidably arranged in the retraction sleeve 10. Thesyringe holder 22 is provided with two or more resilient syringe holderarms 23 arranged distally. The syringe holder arms 23 have a respectiveinclined surface for bearing against a second shoulder 24 in the plunger9 arranged proximally from the first shoulder 19. In the initialposition shown in FIGS. 1A-B the syringe holder arms 23 are supported byan inner surface (not illustrated) of the housing 2 so they cannot flexoutward and the second shoulder 24 cannot slip through. In order tosupport the syringe holder arms 23 at the housing 2 a respective numberof apertures are provided in the retraction sleeve 10.

Two resilient first clips 2.1 are arranged in the housing 2 which engagestops 22.1 on the syringe holder 22 so as to prevent translation of thesyringe holder 22, the syringe carrier 7, the syringe 3 and the needle 4in proximal direction P. Since the syringe holder arms 23 are kept fromflexing out, the load of the drive spring 8 is statically resolvedthrough the decoupling member 14, the plunger 9 and the syringe holder22 into the first clips 2.1 in the housing 2.

A lateral trigger button 20 is arranged laterally on the housing 2 witha pivot 20.1 near its proximal end. In the as delivered configuration inFIGS. 1A-B the trigger button 20 is flush with the housing 2 so itcannot be depressed.

A skin interlock sleeve 25 is telescoped in the proximal end P of thehousing 2. An interlock spring 26 for biasing the interlock sleeve 25 inproximal direction P is arranged between the housing 2 and the interlocksleeve 25. The syringe carrier 7 is telescoped in a proximal portion25.1 of the interlock sleeve 25. A distal portion 25.2 of the interlocksleeve 25 has a greater diameter than the proximal portion 25.1. Thesyringe holder 22 is telescoped in the distal portion 25.2. The distalportion 25.2 exhibits a lug 25.3 and a third ramp 25.4 for interactingwith the trigger button 20. The lug 25.3 is caught between two ramps20.2, 20.3 arranged inwardly in the trigger button 20.

In order to start an injection the proximal end P of the auto-injector 1has to be pressed against the injection site, e.g. a patient's skin. Asa result the interlock sleeve 25 translates in distal direction D intothe housing 2 (see FIG. 2) until the interlock sleeve 25 is flush withthe proximal end P of the housing 2. The lug 25.3 also moves in distaldirection D along the second ramp 20.3 of the trigger button 20 thusrotating the trigger button outwardly in such a manner that the triggerbutton 20 laterally emerges from the housing 2 (see FIG. 2).

The trigger button 20 has now been moved to a position where if pushedit will release the drive spring 8 in order to insert the needle 4 intothe injection site and to inject the medicament M.

If the auto-injector 1 is removed from the injection site withoutoperating the trigger button 20 the interlock sleeve 25 will translateback into its proximal position under load of the interlock spring 26.The lug 25.3 will slide along the first ramp 20.2 and pull the triggerbutton 20 back into the position as in FIGS. 1A-B.

The lug 25.3 is resiliently arranged in the interlock sleeve 25 in sucha manner that it may be pushed radially inwards. As long as theinterlock sleeve 25 is in its proximal position as in FIGS. 1A-B the lug25.3 is prevented from flexing inwards by the retraction sleeve 10. Whenthe interlock sleeve 25 is pushed into the housing 2 as in FIG. 2 thelug 25.3 reaches an aperture 10.1 in the retraction sleeve 10 allowingit to flex inwards. If the interlock sleeve 25 is kept pressed againstthe injection site and the trigger button 20 is being depressed the lug25.3 will be pushed inwards through the aperture 10.1. The resilience ofthe lug 25.3 has to be chosen so as to ensure that the force required tokeep the interlock sleeve 25 pressed does not exceed a convenient levelfor the user since the counteracting force is the sum of the springforce of the interlock spring 26 and the force created by the lug 25.3trying to slide along the second ramp 20.3.

When the lug 25.3 has entered the aperture 10.1 the skin interlocksleeve 25 is prevented from returning into its proximal position.

If the trigger button 20 was depressed with the interlock sleeve 25 onlypartially translated into the housing 2 the lug 25.3 would not yet havereached the aperture 10.1 so it could not flex inwards. Instead,depressing the trigger button 20 would force the interlock sleeve 25back into its proximal position due to the engagement of the lug 25.3with the second ramp 20.3.

When the trigger button 20 is pushed in the situation shown in FIG. 2,the lug 25.3 is pushed radially inwards. A pin 20.4, inwardly arrangedon the trigger button 20, is pressed against the third ramp 25.4 in sucha manner that the interlock sleeve 25 is translated further in distaldirection D into the housing 2, as shown in FIG. 3. This movement willresult in a further flexing of the lug 25.3, as it slides along thesecond ramp 20.3. This position cannot be reached by just pushing theinterlock sleeve 25 against the injection site. A distal end of thedistal portion 25.2 now reaches the clips 2.1 and pushes them outwardsthus decoupling the syringe holder 22 from the housing 2 and releasingthe drive spring 8.

The second shoulder 24 pushes the syringe holder 22, syringe carrier 7and syringe 3 forward in proximal direction P while no load is exertedonto the stopper 6. The hollow needle 4 appears from the proximal end Pand is inserted into the injection site.

The forward movement continues until the syringe holder 22 bottoms outat a front face 35 of the retraction sleeve 10. The travel from theinitial position up to this point defines an injection depth, i.e.needle insertion depth.

When the syringe holder 22 has nearly bottomed out, the resilientsyringe holder arms 23 have reached a widened portion 2.2 of the housing2 where they are no longer supported by the inner wall of the housing 2.However, since the force required to insert the needle 4 is relativelylow the second shoulder 24 will continue to drive forward the syringeholder 22 until proximal travel is halted at the front face 35. At thispoint the syringe holder arms 23 are flexed out by the continued forceof the second shoulder 24 and allow it to slip through. Now the plunger9 no longer pushes against the syringe holder 22 but against the stopper6 for expelling the medicament M from the syringe 3 and injecting itinto or through the patient's skin.

When the stopper 6 has nearly bottomed out in the syringe 3 thedecoupling member 14 has reached a position where it pushes against thelatches 12 in a manner to decouple the retraction sleeve 10 from thehousing 2. Thus the drive spring 8 is no longer grounded with its distalend in the housing 2 by the latches 12. Instead, as soon as thedecoupling member 14 has bottomed out at a second abutment 33 in thehousing 2 the proximal end of the drive spring 8 gets grounded in thehousing 2 while its distal end is pulling the retraction sleeve 10 indistal direction D.

Just before the decoupling member 14 decouples the retraction sleeve 10from the housing 2 the decoupling arms 18 reach an aperture 10.1, 10.2in the retraction sleeve 10 so they are no longer kept from being flexedoutward. The decoupling arms 18 are thus pushed outward by the firstshoulder 19 pushing against its ramped surfaces so the first shoulder 19can slip through in distal direction D as soon as the decoupling member14 has hit the second abutment 33.

Although the latches 12 are disengaged now, the retraction sleeve 10 maynot yet slide in distal direction D because of the lug 25.3 engaged inthe aperture 10.1 so the retraction sleeve 10 is trying to pull theinterlock sleeve 25 in distal direction D which is prevented by thethird ramp 25.4 distally abutting against the housing 2.

If the auto-injector 1 is taken away from the injection site and theuser releases the trigger button 20 the lug 25.3 re-emerges from insidethe retraction sleeve 10 so the retraction sleeve 10 gets disengagedfrom the interlock sleeve 25 and may now translate in distal directionD. A spring means may be arranged for actively pulling the triggerbutton 20 outwards in this situation. In an alternative embodiment thelug 25.3 may project outwards with an inclination in proximal directionP so as to allow the retraction sleeve 10 to push it outwards onretraction.

The syringe holder 22 is taken along in distal direction D by theretraction sleeve 10, e.g. by a front face 35. Thus the syringe 3 andneedle 4 are retracted into a safe position inside the housing 2, e.g.into the initial position. The plunger 9, no longer bearing against thedecoupling arms 18 is pulled back, too.

The housing 2 may have at least one viewing window for inspecting thesyringe 3.

The auto-injector 1 may preferably be used for subcutaneous orintra-muscular injection, particularly for delivering one of ananalgetic, an anticoagulant, insulin, an insulin derivate, heparin,Lovenox, a vaccine, a growth hormone, a peptide hormone, a proteine,antibodies and complex carbohydrates.

1. Auto-injector (1) for administering a dose of a liquid medicament(M), comprising: an elongate housing (2) arranged to contain a syringe(3) with a hollow needle (4) and a stopper (6) for sealing the syringe(3) and displacing the medicament (M), the housing (2) having a distalend (D) and a proximal end (P) with an orifice intended to be appliedagainst an injection site, wherein the syringe (3) is slidably arrangedwith respect to the housing (2), spring means (8) capable of, uponactivation: pushing the needle (4) from a covered position inside thehousing (2) into an advanced position through the orifice and past theproximal end (P), operating the syringe (3) to supply the dose ofmedicament (M), and retracting the syringe (3) with the needle (4) intothe covered position after delivering the medicament (M), activatingmeans (20) arranged to lock the spring means (8) in a pressurized stateprior to manual operation and capable of, upon manual operation,releasing the spring means (8) for injection, wherein the spring means(8) is a single drive spring (8) in the shape of a compression springarranged to be grounded at a distal end (8.1) in the housing (2) foradvancing the needle (4) and for injecting the dose of medicament (M)via a plunger (9) and wherein the drive spring (8) is arranged to haveits ground in the housing (2) switched to its proximal end (8.2) forretracting the syringe (3), characterized in that the activating means(20) is arranged as a trigger button (20) laterally arranged on thehousing (2).
 2. Auto-injector (1) according to claim 1, characterized inthat the trigger button (20) is pivoted in the housing (2) and arrangedto be rotated when operated.
 3. Auto-injector (1) according to one ofthe claim 1 or 2, characterized in that an interlock sleeve (25) istelescoped in the proximal (P) end of the housing (2), the interlocksleeve (25) translatable in longitudinal direction between a proximalposition and a distal position and biased in proximal direction (P) in amanner to protrude from the housing (2) in the proximal position,wherein the interlock sleeve (25) is arranged to be translated from itsproximal position into an intermediate position when pressed against theinjection site, wherein the trigger button (20) is arranged to push theinterlock sleeve (25) from the intermediate position into the distalposition thus releasing the drive spring (8).
 4. Auto-injector (1)according to claim 3, characterized in that in its proximal position theinterlock sleeve (25) is arranged to hold the trigger button (20) in adepressed position, wherein translation of the interlock sleeve (25)into the intermediate position causes the trigger button to emerge fromthe housing (2) into a ready position.
 5. Auto-injector (1) according toone of the claim 3 or 4, characterized in that the interlock sleeve (25)in its intermediate and/or distal position is arranged to preventrelease of the distal ground of the drive spring (8).
 6. Auto-injector(1) according to one of the claims 3 to 5, characterized in that aretraction sleeve (10) is axially movable arranged in the housing (2),wherein the drive spring (8) is arranged inside the retraction sleeve(10) with its distal end bearing against a distal end face (13) and withits proximal end bearing against a thrust face (17) of a decouplingmember (14), wherein a resilient lug (25.3) on the interlock sleeve (25)is arranged to be engaged with the retraction sleeve (10) by the triggerbutton (20) being depressed when the interlock sleeve (25) is in itsintermediate or distal position so as to prevent the retraction sleeve(10) from translating in distal direction (D).
 7. Auto-injector (1)according to claim 6, characterized in that the lug (25.3) is engagedbetween two ramps (20.2, 20.3) on the trigger button (20) in such amanner that the trigger button (20) is pulled into the depressedposition upon translation of the interlock sleeve (25) into its proximalposition by the lug (25.3) sliding along the first ramp (20.2) and thatthe trigger button (20) is pushed into its ready position by the lug(25.3) sliding along the second ramp (20.3).
 8. Auto-injector (1)according to one of the claims 3 to 7, characterized in that a thirdramp (25.4) is arranged on the interlock sleeve (25) for being engagedby a pin (20.4) on the trigger button (20) when the trigger button (20)is being pressed with the interlock sleeve (25) in its intermediateposition such that the pin (20.4) slides along the third ramp (25.4) andtranslates the interlock sleeve (25) into its distal position. 9.Auto-injector (1) according to one of the preceding claims,characterized in that a tubular syringe carrier (7) is arranged forholding the syringe (3) and supporting it at its proximal end, thesyringe (3) and the syringe carrier (7) arranged for joint axialtranslation, wherein the syringe carrier (7) is telescoped in theinterlock sleeve (25).
 10. Auto-injector (1) according to one of theclaims 6 to 9, characterized in that at least one latch (12) is providedfor axially fixing the retraction sleeve (10) in a maximum proximalposition, wherein the decoupling member is arranged (14) to decouple thelatch (12) when being moved in proximal direction (P) nearly into amaximum proximal position, thus allowing the retraction sleeve (10) tomove in distal direction (D) and retract the needle (4). 11.Auto-injector (1) according to one of the claims 6 to 10, characterizedin that at least two resilient decoupling arms (18) are arranged at thedecoupling member (14), the decoupling arms (18) having inner rampedsurfaces bearing against a first shoulder (19) of the plunger (9) inproximal direction (P), wherein the resilient decoupling arms (18) aresupportable by an inner wall of the retraction sleeve (10) in order toprevent the decoupling arms (18) from being flexed outward and slip pastthe first shoulder (19) and wherein at least one aperture (10.1, 10.2)is arranged in the retraction sleeve (10) allowing the decoupling arms(18) to be flexed outward by the first shoulder (19) thus allowing thefirst shoulder (19) to slip through the decoupling arms (18) in proximaldirection (P), wherein the plunger (9) is arranged for pushing thesyringe (3) and/or the stopper (6) in proximal direction (P). 12.Auto-injector (1) according to one of the claims 6 to 11, characterizedin that the syringe (4) is arranged for joint axial movement with asyringe holder (22) which is slidably arranged in the retraction sleeve(10), wherein the syringe holder (22) is provided with at least tworesilient syringe holder arms (23) arranged distally, the syringe holderarms (23) having a respective inclined surface for bearing against asecond shoulder (24), which is arranged at the plunger (9) proximallyfrom the first shoulder (19) wherein the syringe holder arms (23) aresupportable by an inner surface of the housing (2) in order to preventthem from being flexed outward and wherein a widened portion (2.2) isprovided in the housing (2) for allowing the syringe holder arms (23) toflex outwards when the syringe holder (22) has nearly reached a maximumproximal position thus allowing the second shoulder (24) to slip throughthe syringe holder arms (23) and to switch load of the drive spring (8)from the syringe (3) to the stopper (6).
 13. Auto-injector (1) accordingto claim 12, characterized in that the syringe holder (22) has at leastone stop (22.1) for being engaged by a resilient first clip (2.1) on thehousing (2) in a manner to prevent translation of the syringe holder(22) in proximal direction (P), wherein the first clip (2.1) is arrangedto decouple from the stop (22.1) upon translation of the interlocksleeve (25) into its distal position.
 14. Auto-injector (1) according toone of the claims 3 to 13, characterized in that a cap is provided atthe proximal end (P) of the housing (2), wherein a sheet metal clip isattached to the cap for joint axial movement and independent rotation,the sheet metal clip arranged to extend through an orifice into theinterlock sleeve (25) when the cap is attached to the interlock sleeve(25), wherein the sheet metal clip incorporates at least two barbssnapped into a circumferential notch or behind a shoulder of aprotective needle shield attached to the hollow needle (4). 15.Auto-injector (1) according to claim 14, characterized in that the capis attachable to the interlock sleeve (25) by a screw connection.